1. Field of the Invention
This invention relates generally to a satellite communications system providing interactive services to end users.
2. Description of Related Art
Direct Broadcast Satellite DBS systems, where service providers broadcast direct to small receiving dishes in the home, are well known. Initially, these were one-way services allowing purely passive reception. More recently, telephone operating companies have started providing a return line through a terrestrial line to accommodate a user return capability for services such as pay per view TV, home shopping, home banking and similar other services; HUGHES DirectTV presently uses a POTS line as a return to carry information relating to the billing of services provided. This solution requires the use of the switched telephone network and is inefficient, especially when it is used to carry small amounts of data such as ordering information and the like.
Some DBS services offer access to the Internet with the downstream data being provided via satellite on a wideband channel and the return path being via a narrow band terrestrial link, usually a conventional POTS telephone line. This arrangement requires a switched telephone circuit and ties up the public switched network even though relatively small amounts of data are transmitted on the return link on an occasional basis.
An object of the invention is to provide an improved interactive direct broadcast system.
According to one aspect of the present invention there is provided an interactive direct broadcast station comprising means for transmitting broadcast signals via satellite to an end user over a wideband satellite link, means for receiving return signals from end users over a separate narrow band satellite return link providing a return path, and means for interpreting said return signals to respond to requests from the end user.
The broadcast signals can be conventional broadcast video signals or multimedia signals from the comprising text, graphics, sound and video. The Internet is an example of a source of multimedia signals, which can be downloaded over the wideband link.
A wideband link is of the type suitable for broadcast purposes, such as the Ku-band allocated for satellite service. A narrowband link is of the type more usually associated with mobile communications, such as the L-band.
The forward broadcast signals are preferably carried in the Ku band, with the return command signals being carried in the L-band, which is typically used for mobile communications. The invention thus combines two, different one-way satellite transmissions using two different satellites. In a preferred embodiment, this invention uses an L-band satellite proximate to the Ku band broadcast satellite to provide a low cost return path from an individual subscriber. It is estimated that up to a million transactions per hour on the L-band satellite can be provided with each 300 kHz circuit. Currently set top boxes on the user premises have a one way path from a satellite dish that allows a receive only function.
This invention thus provides an inexpensive narrow band transmitter to the system which provides a low cost return. It is estimated that the cost of a single transaction is a small fraction of the cost of a transaction using POTS.
The associated cost using an L-band satellite for low rate data transmission is less than the cost of using Ku-band satellites for high speed return data transmission; L-band transmitters can be at low cost incorporating a low signal level with an antenna having low gain; L-band systems are coordinated to cope with low level wide beam broadcast signals, thus adjacent satellite interference problems can be overcome.
In a preferred embodiment of this invention CDMA (Code division Multiple Access) is used to ensure a lowest possible RF transmit level for a quantity of information that is transmitted on the return link, thereby providing return capacity at low cost. The invention provides a new combination of the receiver and transmitter with CDMA L-band operating simultaneously in conjunction with a broadcast signal in the Ku band. A specific and preferred embodiment of this invention relates to its applicability to existing home satellite dishes that can be adapted at a low cost to conform with the teachings of this invention.
The system includes a narrow beam accurately directed Ku-band antenna (currently present in DBS systems), and in accordance with this invention a second low gain wide-beam L-band antenna. The L-band antenna may be independent of the narrow beam antenna, or it may be incorporated with the DBS antenna, using the dish or a reflector. The latter embodiment produces a very wide beam at L-band because the reflector is small in terms of L-band wavelengths.
The L-band antenna can be mounted in conjunction with the narrow beam antenna, preferably on the same dish, for example, near its periphery because the L-band antenna does not make use of the focussing characteristics of the dish and does not have to be pointed accurately.
Alternatively, the L-band antenna may be independent of the Ku-band antenna. It may be mounted on the periphery of the Ku-band dish or alternatively, remote from it in the form of a microstrip patch or short helix of several turns providing suitable, relatively low gain for this application.
This invention combines the advantages of satellite mobile communications in the L-band with the advantages of the broadcasting capabilities of the Ku band. The system provides a high data rate broadcast signal out (on the Ku band) and a low data rate return signal (on the L-Band). Furthermore, this can be achieved with existing satellites.
Another novel and inventive aspect of this invention lies in the arrangement of components disposed between a set top-box and the antenna units. Essentially these components comprise a CDMA module providing modulation of the L-band return signal. This module further includes a Tx unit for the L-band.
According to another aspect of the invention there is provided a home direct broadcast receiving system, comprising a receiver for receiving wideband broadcast signals from a hub station via satellite on a wideband link, means for generating return signals for making specific requests to said hub station, and a transmitter for transmitting said return signals via satellite back to said base station over a separate narrowband link.
According to a still further aspect of the invention there is provided a method of providing an interactive broadcast service comprising the steps of transmitting broadcast signals via a wideband satellite link to end users, receiving return signals from said users transmitted over a separate narrowband satellite link, and responding to said return signals to provide services requested by said users.
The invention thus provides a communications system that comprises two different satellites each configured to operate to form a single communications system wherein each satellite is are in one-way communications but together, provide two way communications. More specifically, an aspect of the invention relates to terminal equipment on the user premises, comprising a small low cost transmitter in a return link in the system.